1. Field of the Invention
The present invention relates to a method of performing flying splices in an unwinding station, and, more particularly, relates to a method of splicing the leader of a new roll of a web roll ("primary roll") on the fly to the end of a preceding (nearly spent) web roll ("secondary roll") from which a web is being unwound for treatment.
2. Description of the Related Art
A method of performing a flying splice may be used at an unwinding station of a paper coater or on other, similar machines serving the treatment or processing of paper webs. The splicing of the two webs to one another must take place at full operating speed and, therefore, requires a very precise control. The operating speed may amount to 1500 m/min and can assume even higher values. This splicing operation is mostly called a "flying splice" in the paper industry. An example of equipment for making a flying splice is disclosed in Voith publication p2827.
It is known that in preparation of a flying splice the primary roll is rotated by means of a drive unit, adapting its peripheral speed as exactly as possible to the momentary operating speed of the machine, and thus to the momentary velocity at which the web unwound so far departs from the secondary roll. A prerequisite is, among others, that the unwinding station feature a braking system which makes it possible to always maintain a certain longitudinal tension (web draw) on the unwinding web. A drive unit which is operated selective as a motor or as a brake is usually provided, at least for the primary roll. But it is understood that the drive unit of the primary roll cannot generate the desired draw on the web unwinding from the primary roll until the flying splice of the web leader of the primary roll to the web end of the secondary roll has taken place.
The drive unit is preferably an electric machine or, as the case may be, a hydraulic machine that can be switched to braking operation.
A difficulty is constituted by the fact that in the prior methods the desired draw in the web unwinding from the primary roll does not build up with sufficient swiftness. Observed is mostly a temporary collapse of the draw immediately after the flying splice.